Coating of photographic elements has been known in the art as has the use of a slide-bead coating apparatus to accomplish the task.
Slide bead coaters are well known in the art to utilize a pressure differential on the upper and lower surfaces of the coating solution to reduce air entrapment and to facilitate the formation of a liquid bead, or bridge, between the surface of the coater and the substrate being coated.
For a given coating solution at a given coating rate the range of operative differential pressure, also known as vacuum range, is defined by an upper limit and a lower limit. Above the upper limit streaks and other defects occur which decreases the usefulness of the final product. Below the lower limit the stability of the bead degrades and the edges of the coating are drawn in towards the center of the coating which is catastrophic. It is the goal of the artisan to maintain an operating differential pressure which is between the upper and lower limits and which will not encroach on either limit when minor operational fluctuations occur.
One of the main goals of a skilled artisan is the ability to achieve higher coating rates. As the coating rate is increased the difference between the upper and lower limits of differential pressure diminishes as described in Zeldes U.S. Pat. No. 4,508,764. Due to this conflict there is an ongoing need in the art for coating compositions which can effectively increase the range of differential pressure.